1. Field of the Invention
This invention relates to a frequency tunable device, more particularly to a frequency tunable device including a substrate and a dielectric film formed on the substrate and made from a Pb1−xBaxZrO3ferroelectric material with a dielectric property being a function of a voltage applied thereto.
2. Description of the Related Art
U.S. Pat. No. 5,589,845 discloses a tunable electric antenna apparatus that includes a component of a thin film ferroelectric material, such as SrTiO3, Pb(Sr, Ti)O3, SrxBa1−xTiO3 (BST), etc. The ferroelectric material has a dielectric property that is a function of a voltage applied to the thin film ferroelectric material. Such a dielectric property enables the ferroelectric material to modulate the dielectric constant and hence the time delay of either microstrip or coplanar delay lines, and allows for use in producing phase shifters, antennas, etc.
BST ferroelectric materials tend to degrade due to the reduction of Ti4+ into Ti3+, which, in turn, results in an increase in dielectric loss. This degradation problem can be alleviated by adding an aliovalent element into the BST ferroelectric materials. The following patents are examples of reducing dielectric loss through the addition of an aliovalent element into the BST ferroelectric materials.
U.S. Pat. No. 5,312,790 discloses a ceramic ferroelectric material consisting essentially of BST and alumina for achieving the desired electric property, such as a low dielectric constant, a low loss tangent, and high tunability. U.S. Pat. No. 5,427,988 discloses a ceramic ferroelectric material consisting essentially of BST and magnesia. U.S. Pat. No. 5,486,491 discloses a ceramic ferroelectric material consisting essentially of BST and zirconia.
Although the addition of an aliovalent element into ferroelectric material can reduce dielectric loss, it also results in reduction in the tunability of the ferroelectric material.
The entire disclosure of U.S. Pat. No. 5,589,845 is incorporated herein by reference.